Various techniques of high-speed jet printing have been widely used in the printing industry. One of the main goals of the applications of these techniques is, under the control of computers, to jet print variable labels, bills, bar codes on continuous papers having color blocks in a fixed interval. In a high-speed jet control system, according to the positions of color blocks, positions of jet printing are often controlled using the following two methods.
I. High Level Software Based Correction Method
A color code sensor detects the color blocks printed on continuous papers and the color blocks are used as reference signals for printing. An encoder outputs pulse signals which are in synchronization with paper motion. Then, the color block interval on the continuous papers can be calculated and the information is delivered to high level control software. After detecting a first color code, the printing unit continuously prints the received image data according to the pulse signals output by the encoder. The software adjusts blank data between valid image data according to the received information of color block spacing, so as to control the printing positions. This method can be easily implemented. When color block spaces are relatively constant, the printing positions of images are generally accurate. However, when difference among color block spaces are relatively large or a color code is undetected during the process of detecting, this method of control of printing positions may be slow to adjust to the correct printing positions. Thus, the printing positions may be erroneous and many defective printing products may be produced.
II. Hardware Based Simple Control Method
The control software transfers the valid image data to be printed to a print control unit. The control software also uses hardware to control the printing positions. A color code sensor detects the color blocks printed on continuous papers and the color blocks are used as reference signals for printing. An encoder outputs pulse signals which are in synchronization with paper motion. After a color code signal is detected, an jet control system delays N encoder pulses according to software configurations so as to start to print a page of image data. After another color code signal is detected, N encoder pulses are delayed again to print a next page of image data. These steps repeat. This method can reduce the burden on the software. Even if the color block spaces vary a bit, the printing can be performed accurately according to the real-time detected color code signals. However, when there are interferences to color code signals or a color code is undetected, there may be false printing or missed printing so that some defective printing products are produced.